This study was carried out to investigate the effect of W substitution on the precipitation behavior of χ and σ phases in super duplex stainless steel. The χ phase was precipitated at the interface of ferrite / austenite phases and inside the ferrite phase at the initial stage of aging. With an increase in the aging time, the volume fraction of the χ phase increased, and then decreased with the transformation from the χ phase to the σ phase. The σ phase was precipitated later than the χ phase, and the volume fraction of x phase increased with the increase in the aging time. The ferrite phase was decomposed into the new austenite (γ2) and σ phases by aging treatment. The decomposition of the ferrite phase into the γ2 and σ phases was retarded by W substitution for Mo. The volume fraction of the χ phase increased and that of the σ phase decreased due to W substitution. The χ and σ phases were intermetallic compounds, which had lower nickel concentration, and higher chromium, molybdenum, and tungsten concentrations. The χ phase has higher molybdenum and tungsten concentrations than those of the σ phase. The amounts of chromium and nickel in the χ and σ phases did not change, but these phases have higher concentrations of molybdenum and tungsten due to W substitution for Mo.

In this study, we investigated the effect of the residual carbides and tempered carbides precipitated by tempering treatment after quenching on the pitting corrosion of mod. 440A martensitic stainless steel. In quenched specimens and tempered specimens after quenching of mod. 440A martensitic stainless steel, the volume fraction of the residual carbides and total carbides decreased with the increase of the austenitizing temperature. Pitting resistance increased with the increase of austenitizing temperature. With the increase of the volume fraction of the residual and total carbides, the pitting resistance of mod. 440A martensitic stainless steel was decreased. The pitting resistance of mod. 0.5C-17Cr-0.5Ni 440A martensitic stainless steel had stronger affected by residual carbides than precipitated carbides produced by tempering.

The finite element analysis of large sized rectangular water tank structures made of stainless steel materials is carried out for various combined load cases. The combined load cases for a large size of 5,000ton are further determined using the specification(KS B　6283) established from the Korean Standards Association. For the better numerical efficiency, the rectangular panels are modelled using the ANSYS program. The numerical results obtained for different load cases show as follows. In order to resist the snow load, it takes the influence of the gap than the size of the column. Also, in order to resist the water pressure, it shall increase the thickness of the wall. But, increasing the thickness of the wall is considerably less economical. Therefore, the angle with big thickness should be placed right next to the wall.

As wrought stainless steel, sintered stainless steel (STS) has excellent high-temperature anti-corrosion even at high temperature of 800ºC and exhibit corrosion resistance in air. The oxidation behavior and oxidation mechanism of the sintered 316L stainless was reported at the high temperature in our previous study. In this study, the effects of additives on high-temperature corrosion resistances were investigated above 800ºC at the various oxides (SiO2, Al2O3, MgO and Y2O3) added STS respectively as an oxidation inhibitor. The morphology of the oxide layers were observed by SEM and the oxides phase and composition were confirmed by XRD and EDX. As a result, the weight of STS 316L sintered body increased sharply at 1000oC and the relative density of specimen decreased as metallic oxide addition increased. Compared with STS 316L sintered parts, weight change ratio corresponding to different oxidation time at 900oC and 1000oC, decreased gradually with the addition of metallic oxide. The best corrosion resistance properties of STS could be improved in case of using Y2O3. The oxidation rate was diminished dramatically by suppression the peeling on oxide layers at Y2O3 added sintered stainless steel.

In this study, nitrogen ions were implanted into STS 316L austenitic stainless steel by plasma immersion ion implantation (PIII) to improve the corrosion resistance. The implantation of nitrogen ions was performed with bias voltages of −5, −10, −15, and −20 kV. The implantation time was 240 min and the implantation temperature was kept at room temperature. With nitrogen implantation, the corrosion resistance of 316 L improved in comparison with that of the bare steel. The effects of nitrogen ion implantation on the electrochemical corrosion behavior of the specimen were investigated by the potentiodynamic polarization test, which was conducted in a 0.5 M H2SO4 solution at 70 oC. The phase evolution and texture caused by the nitrogen ion implantation were analyzed by an X-ray diffractometer. It was demonstrated that the samples implanted at lower bias voltages, i.e., 5 kV and 10 kV, showed an expanded austenite phase, γN, and strong (111) texture morphology. Those samples exhibited a better corrosion resistance.

본 연구에서는 스테인리스강을 사용하여 전형적인 3-전극 시스템의 순환전류전압법으로 트리에탄올아민(TEA) 용액 중에서 전류-전압 곡선을 측정하였다. 스테인리스강은 작업 전극으로, Ag/AgCl 전극은 기준 전극으로, 그리고 백금 선은 상대 전극으로 각각 사용하였고, 그 결과, 트리에탄올아민 용액에서의 스테인리스강의 C-V 특성은 순환전류전압법으로부터 산화전류에 기인한 비가역 공정으로 나타났다. 부식억제제의 확산계수의 효과는 농도 증가에 따라 감소하였다. 그리고 부식억제 효과는 농도 0.5 N의 NaClO4, 2.5x10-3 M TEA용액에서 가장 컸으며, 1.5 N NaClO4, 1.0x10-3 M TEA용액에서 가장 낮았다.

The finite element stress analysis of large sized rectangular water tank structures made of stainless steel materials is carried out for various combined load cases. The combined load cases for a large size of 5,000ton are further determined using the specification(KS B　6283) established from the Korean Standards Association. The changed water capacity due to the size of reservoirs could be heavily dependent for evaluating seismic effects, especially for large reservoirs. For the better numerical efficiency, the rectangular panels are modelled using the ANSYS ADPL module. The numerical results obtained for different load cases mainly show the effect of the interactions between the different load combination and other various parameters, for example, the water capacity, and different stainless steel materials. The structural performance for various load combinations is also evaluated.

Fatigue crack growth rate tests were conducted as a function of temperature, dissolved hydrogen (DH) level, and frequency in a simulated PWR environment. Fatigue crack growth rates increased slightly with increasing temperature in air. However, the fatigue crack growth rate did not change with increasing temperature in PWR water conditions. The DH levels did not affect the measured crack growth rate under the given test conditions. At 316 oC, oxides were observed on the fatigue crack surface, where the size of the oxide particles was about 0.2 μm at 5 ppb. Fatigue crack growth rate increased slightly with decreasing frequency within the frequency range of 0.1 Hz and 10 Hz in PWR water conditions; however, crack growth rate increased considerably at 0.01 Hz. The decrease of the fatigue crack growth rate in PWR water condition is attributed to crack closure resulting from the formation of oxides near the crack tips at a rather fast loading frequency of 10 Hz.

As well-known wrought stainless steel, sintered stainless steel (STS) has excellent high-temperature anticorrosion even at high temperature of 800ºC, and exhibits good corrosion resistance in air. However, when temperature increases above 900ºC, the corrosion resistance of STS begins to deteriorate and dramatically decreases. In this study, the effects of phase and composition of STS on high-temperature corrosion resistances are investigated for STS 316L, STS 304 and STS 434L above 800ºC. The morphology of the oxide layers are observed. The oxides phase and composition are identified using X-ray diffractometer and energy dispersive spectroscopy. The results demonstrate that the best corrosion resistance of STS could be improved to that of 434L. The poor corrosion resistance of the austenitic stainless steels is due to the fact that NiFe2O4 oxides forming poor adhesion between the matrix and oxide film increase the oxidation susceptibility of the material at high temperature.

The effect of retained and reversed austenite on the damping capacity in high manganese stainless steel with two phases of martensite and austenite was studied. The two phase structure of martensite and retained austenite was obtained by deformation for various degrees of deformation, and a two phase structure of martensite and reverse austenite was obtained by reverse annealing treatment for various temperatures after 70 % cold rolling. With the increase in the degree of deformation, the retained austenite and damping capacity rapidly decreased, with an increase in the reverse annealing temperature, the reversed austenite and damping capacity rapidly increased. With the volume fraction of the retained and reverse austenite, the damping capacity increased rapidly. At same volume of retained and reversed austenite, the damping capacity of the reversed austenite was higher than the retained austenite. Thus, the damping capacity was affected greatly by the reversed austenite.

In this study, we investigated the precipitation behavior of the R-phase precipitated at the initial stage of aging and its effect on the pitting corrosion of 25%Cr-7%Ni-4%Mo super duplex stainless steel. The R-phase in super duplex stainless steel was mainly precipitated at the interface of ferrite/austenite phases and inside of the ferrite phase during the initial stage of aging, and it was transformed into the σ-phase with an increase in aging time. The ferrite phase was decomposed into a new austenite phase and σ-phase. The R phase was an intermetallic compound, which represented a lower Ni and higher Mo than the matrix, and also had a higher Mo and Cr concentration than the σ phase. With an increasing aging time, the pitting potential Ep was increased slowly by the precipitation of the R-phase, and it was then steeply decreased by the precipitation of the σ-phase. The R-phase was decreased the pitting potential, but its effect was smaller than effect of σ-phase.

Automatic continuous manufacturing system is necessary to raise the productivity and strengthen the competitiveness in the wire manufacturing. The automatic wire cutting technology is an important element to link various processes and it is crucial technology to obtain high accuracy and quality of the wire. This study was performed to develop an automatic stainless steel wire cutting equipment that is consist of the first and second cutting equipments besides related devices to cut stainless steel wire. This wire cutting equipment can cut wire with high accuracy, and it can prevent sintering and discoloration

In this study, we investigated the precipitation behavior of the R-phase precipitated at the initial stage of aging and its effects on the mechanical properties of 25%Cr-7%Ni-2%Mo-4%W super duplex stainless steel. The R-phase was mainly precipitated at the interface of ferrite/austenite phases and inside of the ferrite phase during the initial stage of aging. It was transformed into the σ-phase with an increase of the aging time. The ferrite phase was decomposed into a new austenite(γ2)phase and the σ-phase by an aging treatment. The R phase was an intermetallic compound showing higher molybdenum and tungsten concentrations than the matrix and also showed higher molybdenum and tungsten concentrations than the σ phase. In the initial stage of aging, precipitation of the R-phase did not change the hardness, the strength and the elongation. The hardness and the strength increased upon a longer aging time, but the elongation rapidly decreased. These results show that the R-phase did not significantly affect the hardness and the strength, though it did influence the elongation.

Fiber laser welding has been developed for precise welding of small and complicate components assembled on the nuclear fuel irradiation test rig. In this research, laser welding characteristics of STS316L, the main material of nuclear fuel test rig, have been studied. Several welding experiments were carried out in lap welding of the tube and the end cap made of STS316L. Process variables such as non-focal length, shield gas, laser frequency and power are optimized and compared with the results of Zircaloy-4.

본 연구에서 고투과도를 갖는 실리카 분리막은 콜로이달 실리카 졸과 고분자형 실리카 졸 두 가지를 DRFF법과SRFF법으로 다공성 금속 지지체 위에 코팅하여 제조되었다. 실리카 졸은 졸-겔법으로 테트라에톡시실란(TEOS)에 의하여 제조되었고, 각각의 졸은 동적광산란법(DLS), 전계방사 주사전자현미경(FE-SEM), 질소 흡착법 등을 이용하여 그 특성을 평가하였다. 다공성 금속 지지체위에 콜로이달 실리카 졸로 중간층을 형성하여 치밀한 구조의 실리카 층을 형성한 후 그 위에 분리층으로 고분자형 실리카 졸을 코팅하여 핀홀을 줄이는 방법으로 기체분리용 분리막을 제조하였다. FE-SEM으로 분리막의코팅 층을 분석한 결과 분리층은 중간층보다 침밀한 구조를 가지고 있음을 확인하였고 기체투과 결과 수소 투과도 (6.63-9.21) × 10-5 mol⋅m-2⋅s-1⋅Pa-1 분포를 보였다.

합성된 스테인레스 스틸에 대한 NATM(New Austria Tunnel Method) 수지의 기계적 특성은 SEM, FT-IR, 인장특성, 그리고 [NCO]/[OH]의 mole %, 입도분석에 의해 측정하였다. 친환경적인 NATM에 관한 관심이 고조됨에 따라 스테인레스 등의 금속에 코팅하는 무용제 도료를 합성하였다. 폴리올, IPDI, 충진제, 실리콘 계면활성제, 촉매 등이 함유된 기존 NATM수지보다 폴리올, MDI, 충진제, 실리콘 계면활성제, 촉매, 가교제가 함유되어 합성된 NATM 수지의 도료가 내구력과 강도가 양호하였다. 견고한 NATM 수지의 기계적 특성은 가교와 [NCO]/[OH]의 mole%가 증가함에 따라 강도가 증가하였다. 결론적으로 NATM의 가교된 미세조직는 스테인레스 스틸 같은 금속물질 코팅에 좋은 물질이다.

The 304 stainless steel powders were prepared by high energy ball milling and subsequently sintered byspark plasma sintering, and the microstructural characteristics and micro-hardness were investigated. The initial size ofthe irregular shaped 304 stainless steel powders was approximately 42 µm. After high energy ball milling at 800 rpmfor 5h, the powders became spherical with a size of approximately 2 µm, and without formation of reaction compounds.From TEM analysis, it was confirmed that the as-milled powders consisted of the aggregates of the nano-sized particles.As the sintering temperature increased from 1073K to 1573K, the relative density and micro-hardness of sintered sampleincreased. The sample sintered at 1573K showed the highest relative density of approximately 95% and a micro-hard-ness of 550 Hv.

전형적인 3-전극 시스템의 순환전압전류법을 사용하여 알킬기를 가진 에탄올아민 용액 중에서 스테인리스에 대한 전류-전압 곡선을 측정하였다. 스테인리스는 작업 전극으로, Ag/AgCl 전극은 기준 전극으로, 그리고 백금선은 상대 전극으로 각각 사용하였다. N-에틸에탄올아민과 N,N-디메틸에탄올아민 용액에서의 스테인리스의 C-V특성은 순환전압전류법으로부터 산화전류에 기인한 비가역 공정으로 나타났다. 부식억제제의 확산계수의 효과는 각각 농도 증가에 따라 감소하였다. 금속의 SEM 이미지로부터 0.5 N의 전해질에서 부식억제제인 N,N-디에틸에탄올아민 (1.0 × 10-³ M)을 첨가한 경우, 구리와 니켈에서 부식억제 효과가 향상되었다.

This study is experimentally investigated whether or not a relationship exists between the mechanical properties anddamping capacity of cold-rolled 316L stainless steel. Deformation-induced martensite was formed with surface relief anddirectionality. With the increasing degree of deformation, the volume fraction of ε- martensite increased, and then decreased,while α'- martensite increased rapidly. With an increasing degree of deformation, tensile strength was increased, and elongationwas decreased; however, damping capacity was increased, and then decreased. Tensile strength and elongation were affectedin the α'- martensite; hence, damping capacity was influenced greatly by ε- martensite. Thus, there was no proportionalrelationship between strength, elongation, and damping capacity.